1. Field of the Invention
This invention relates to a method for detecting pathological macromolecules in body fluids, and more specifically to a method for early detection of pathological, aggregation-specific proteins, the accumulation of which in body tissues leads to organ failure, disease and even death.
2. Background of the Invention
Many diseases affecting organ systems and vessels having extremely narrow passageways are related to the deposition of large macromolecules in those systems and vessels. Susceptible organ systems include the spleen, heart, kidney, liver, lungs, and related vessels.
Renal and systemic diseases of the kidney result from the pathologic deposition of monoclonal antibody light chains, i.e., Bence Jones proteins. Myeloma (cast) nephropathy, light-chain deposition disease, and AL amyloidosis, result from cast formation, basement membrane precipitates, or fibrils, respectively.
Multiple myeloma is a form of cancer principally associated with the elderly. With multiple myeloma, certain cells of the bone marrow become cancerous and multiply, causing production of excessive amounts of a single type of immunoglobulin, which appears in the blood. In such patients, the urine contains large amounts of Bence Jones protein, which is the light chain portion of IgG. Bench Jones protein is found as covalent dimers of light chains, free light chains in monomer/dimer equilibrium, and sometimes as light chain fragments corresponding to either the variable (V) domain or constant (C) domain portions of the protein. These light chains are made in excess of the heavy chains and then excreted. In most cases, the cancerous, dispersed monoclonal proliferation of cells continue to produce antibodies during the disease.
Immunoglobulins are produced by a specialized type of cell known as the B lymphocyte or B cell. A particular B cell and its descendents are known as a clone. In principle, all B cells in a clone are identical and synthesize identical antibodies; i.e., the cells are comprised of identical light chains and identical heavy chains. The antibodies produced by a single clone all have the same physicochemical properties including solubility, stability, and antigen specificity. The natural function of antibodies is to bind to antigens such as bacteria and viruses and thereby enable the body to evoke an immune response and eliminate the pathogen. Because of the large number of potential pathogens, the body has a large number of different B cell clones each of which produces antibodies of different physicochemical properties because the amino acid sequences of the V domains of light and heavy chains are different from those found in other clones.
Multiple myeloma is a cancer that results from the malignancy of a particular clone of B cells. Although the cancer-causing process is unknown, it effectively selects at random a single cell out of potentially hundreds of thousands of choices to generate the malignancy. As a result, although the antibodies produced by a single patient are chemically homogeneous because they are the product of a single clone of cells (monoclonal), the proteins produced by any two patients are different and have different physicochemical properties. It is these differences that leads to different pathological risks for individual patients.
Certain Bence Jones proteins are "malignant" in that they form toxic proteinaceous deposits in the form of renal tubular casts, nonfibrilar basement membrane deposits, and fibrilar amyloid deposits. Aside from the kidney, the latter two types of deposits also may appear in the spleen, heart, other organs or systemically throughout the body. Other Bence Jones proteins are "benign" in that they cause no obvious disease. The "malignant" proteins or their larger products of interaction may block or reduce the function of the organ; as such, the pathology associated with this problem may be considered as a biophysical disease. Death often occurs as a result of this biophysical phenomenon. The ratio of mortality from multiple myeloma in the 70-74 year old age group to that in the 20-24 year old age group is approximately 2000. Between the years 1950 and 1980, the age-corrected mortality rate of multiple myeloma more than doubled. As the population continues to age, the medical significance of multiple myeloma will increase.
Biopsy is one of the few accurate methods used to diagnose protein-deposition disease. However, weak patients often cannot withstand such an invasive procedure for what may turn out to be a bad hunch on the part of attending physicians.
A need exists in the art for a method to rapidly determine the presence of potentially pathological proteins in bodily fluids. There is also a need to diagnose any predisposition for such disease well in advance of its manifestation so that dietary and other medical intervention can be used to stymie subclinical, morphological changes. The method must be accurate, noninvasive and rapid.